1. Field of the Invention
The present invention relates to inspection of manufactured medical devices; more particularly, this invention relates to automated detection and evaluation of defects in manufactured medical devices.
2. Background of the Invention
The inspection of medical devices can be a labor intensive process. One particular area where there is a substantial amount of manual labor required for inspection is the inspection of self-expanding or balloon-expandable stents. These devices must be carefully inspected by a technician during various stages of manufacture, including when they are cut from tubes, for example, or when a drug-eluting coating is applied. The inspection process is laborious and time-consuming for both metal and polymer stent types. The later category, in particular, requires close inspection due to, e.g., the susceptibility of failure when a micro-crack appears in a polymer strut. Typically, the inspection process involves the viewing of the surfaces of a manufactured stent under a microscope by a technician, who decides whether the stent should be rejected or accepted based on his/her own judgment.
On the one hand, a stent will usually have one or more defects, but in many cases these defects are negligible. On the other hand, a defect may seem innocuous but upon closer inspection there appears a potentially serious problem with the stent, e.g., a micro crack appearing in a high stress region of a polymer stent. The stent is accepted in spite of the defect, in the former case, and rejected as unusable in the later case.
Since the days when clinical side-effects resulting from defective stents were first reported, a thorough stent inspection standard has been adopted throughout the industry. To the inventor's knowledge this stent inspection is still performed manually by a technician hunched over a microscope inspecting every surface of a stent. Despite this inefficiency, the art has yet to produce a satisfactory solution to the inspection problem for medical devices.
It is critical to determine whether there are defects, which requires expertise in being able to visually spot defects that appear only at the microscopic level, e.g., a micro-crack in a stent, coating irregularity, etc. Stents have complex patterns of interacting structural members and measure in lengths of millimeters. Moreover, not all defects will cause problems. The challenge is, therefore, not simply a matter of finding a defect. Rather, the industry requires one to differentiate between defects that are likely to cause problems verses defects that may be ignored, so that usable stents are not disregarded needlessly due to a minor defect.